(a) Field of the Invention
This invention generally relates to systems for carrying out remote hydraulic extraction (mining) of rocks, minerals and industrial materials, and more specifically, but not by way of limitation, to hydraulic borehole mining (BHM) systems, applied through non-vertical (near-horizontal) boreholes which allow simplification of the technology and reduction of drilling procedures by increasing the volume of material to be mined per borehole.
This BHM method is intended for extraction of mineral resources and industrial materials and creation of underground caverns through inclined boreholes, including deviated boreholes. This technology can be applied from the earth surface, as well as from underground mines, open pit floors, valleys and from water surfaces. The technology can be used in geological exploration for bulk sampling; in building of underground storage; in stimulation of in-situ leaching, oil, gas and water production; in construction of custom foundation, underground collectors, walls, and barriers; etc. The technology can be used to solve environmental problems, underground firefighting and fire prevention and other applications requiring remote operating and control of the mining processes.
(b) Discussion of Known Art
Borehole mining as a remote underground mining method is based on water jet cutting of rock material. It is accomplished by pumping high-pressure water down to the working area from the surface (pit floor, underground mine or floating platform) by a BHM tool, lowered into a pre-drilled borehole. At its bottom, the tool has a hydromonitor with a nozzle, which creates a water jet to cut rock and create slurry. The created slurry is simultaneously pumped back to the surface by the eductor, located mainly at the tool""s very bottom. The slurry is then separated in a settling pit or tank, and clarified water is pumped down again to the borehole. While extracting rock material, underground caverns (stopes) can be created. The shape and proportions of these stopes are the matter of tool manipulation in a hole, which is simply a combination of rotating the tool and sliding it along the borehole axis. Being sufficiently extended along the borehole, these caverns may be used as underground storage for oil, gas and other gaseous or liquefied products.
BHM boreholes are drilled mostly vertically. There are several factors requiring this orientation. First, the BHM tool is rotated in a borehole while mining. During this rotation, the water jet is xe2x80x9cflyingxe2x80x9d just over the slurry level, which naturally is strictly horizontal. Thus, if the tool has even a slight deviation from the vertical axis, the water jet may hit the water (slurry), which will break the jet and decrease its rock cutting ability.
Another problem is transportation of the slurry from the rock face to the tool""s eductor zone or borehole sump. If the tool is deviated from the vertical axis, then one side of the cavern created will be above the other. The transporting slope from one side will therefore be steeper than from the other, creating uneven conditions for slurry transportation and making a created cavern asymmetrical. It finally may affect the stability of the cavern and cause an unwanted collapse.
The vertical (chimney-like) ore body shape would be the most appropriate for conventional vertical borehole mining. This requires drilling a borehole along a vertical axis followed by extraction of the ore. Meanwhile, most of the known sedimentary deposits and ore bodies have horizontal or near-horizontal shape and orientation. Except Kimberlite xe2x80x9cpipesxe2x80x9d and a few known unique-shape deposits, all other ore bodies could be qualified as horizontal or being developed by horizontal layers. In order to develop them by vertical BHM, numerous equally spaced boreholes have to be drilled. The distance (D) between boreholes usually equals the BHM tool reach diameter (usually up to a max. of 9-11 m) plus some offset, if required for between-stope pillars (2-4 m), so then D=10+3=13 m.
It is easy to calculate, for example that the number of boreholes required for the development of an ore body whose plane square area equals to 10,000 m2 will be:
10,000/(13xc3x9713)=59 boreholes, which is a significant number for a 100 mxc3x97100 m area. This means that for the development of those types of ore bodies, using conventional BHM, a massive drilling stage will increase the project budget. Additionally, since every drill hole requires surface area, most if not all of the surface over the deposit will be disturbed.
Also, most geo-technological and environmental tasks require near-horizontal development and/or construction (ground walls, drainage collectors and so on), requiring massive drilling along those features. It could be more easily created through a single deviated borehole or one drilled from underground works.
Conventional (vertical) borehole mining suffers from another disadvantage. The vertical BHM is accomplished by moving the tool up (bottom-up schematic) or down (top-down schematic) the borehole. Both of these schematics have problems. While moving the tool xe2x80x9cbottom-upxe2x80x9d, the eductor is moving together with the tool away from the stope bottom (sump) area, where slurry will collect. In this configuration the material cut from the rock face is free-falling and accumulating on the bottom instead of being removed from the stope.
While moving the tool xe2x80x9ctop-downxe2x80x9d the tool becomes suspended in the stope. Any collapse or fall-off from the stope wall may easily damage the tool, even to a point where it may become impossible to remove the tool from the hole.
Additionally, while increasing the diameter of a cavity, the roof or portion(s) of it may collapse while mining. These collapsed rock masses may interfere with the water jet and be an obstacle on its trajectory between the nozzle and the cutting rock face. In other words, these collapses may prevent BHM process from achieving the maximum possible diameter of the cavern and thus decrease the entire BHM effectiveness. To overcome these disadvantages, a mining technology using inclined, deviated, or near-horizontal boreholes is required, and is the topic of this invention.
The U.S. Pat. No. 4,536,035 to Huffinan et al covers a double-drill hydraulic mining method which includes drilling a slant borehole along the production vein footwall and a vertical borehole to intersect the bottom of the first one. Then, the mining tool is inserted into the slant borehole, while a pumping unit is inserted into the vertical borehole. The mining tool includes a water jet nozzle which cuts the rock while the tool is slowly rotated back-and-forth through 180xc2x0 and pulled slowly out from the borehole. The created slurry rolls down to the bottom part of the vertical borehole to the pumping unit and is delivered to the surface. This method allows the creation of extended caverns along the slant borehole.
The Huffman method of mining suffers from the following disadvantages:
First, a large diameter (24xe2x80x3) borehole has to be drilled to remove the mined material. This increases drilling procedures and overall mining cost.
Second, the drilling of two boreholes requires a certain footprint on the earth""s surface to be developed for drill rig sites, sediment ponds and the other equipment. This is not always possible due to the natural landscape, agricultural and environmental requirements and/or other land surface usage (city or industrial zone, private lands and so on).
Third, the Huffman method has a limited application area. It can be applied xe2x80x9cat an angle-pitched mineral vein extending downwardlyxe2x80x9d, as it is stated in their claim 1. In other words, application in an irregular-shaped ore body will not be as effective as in that of a sloping vein. Additionally, this method is developed to mine seams xe2x80x9chaving dip angle ranging from 25xc2x0 to 75xc2x0xe2x80x9d as it explained in their Detailed Description. Thus, this method cannot be applied in seams lying in a xe2x80x9cflatxe2x80x9d range between 0xc2x0 and 25xc2x0.
Fourth, this method requires a reverse rotation of the tool within 180xc2x0 to create a domed cavern, extended along the slant borehole. This reverse rotation tool operation requires special joints between the tool""s sections to prevent their unscrewing. These joints are available industry-wide, but their usage makes the tool""s construction more complicated, heavier, and larger diameter. This in turn requires drilling of a larger diameter borehole, raising the overall cost of mining.
The U.S. Pat. No. 4,226,475 to Frosch, et al covers another remote underground mineral extraction method. This method requires drilling of a vertical borehole toward a production zone and then deviation of that borehole along the production zone. Then, similar to the Huffman method, a vertical borehole is drilled to intersect the end zone of the first borehole to pump up the pregnant slurry developed by the mining tool while removing it from the deviated borehole. Unlike the Huffinan method, this method allows development of near-horizontal layers, but still suffers from almost the same set of disadvantages.
Additionally, this method is extremely expensive due to the usage of custom designed self-walking support vehicles. It is also an extremely complicated technology, as it requires numerous precise remote operations (cutting of drainage tunnels, tool positioning and so on).
Also, Frosch suggests steering of the mining head attached to the flexible high pressure hose by steering nozzles in a manner similar to operating a spacecraft in weightlessness. According to the invention, turning on a side nozzle will steer the inserting tool to the opposite direction. The force of gravity, which will try to turn the heavy working head down, is much greater than the reactive force from the steering nozzle. More likely, the head will constantly have a tendency to dip downward, thus making it difficult to steer.
Finally, in practice, while inserting the mining head into the borehole, the drill pipe string is usually twisted. Due to this twisting, the orientation of the mining head can be easily lost. Without knowing the current position of the head, its further orientation becomes nonsensical.
The U.S. Pat. No. 4,245,699 xe2x80x9cMethod for In-situ Recovery Of methane From Deeply Buried Coal Seamsxe2x80x9d to Johannes W. M. Steeman is also known. Steeman offers to drill xe2x80x9c . . . at least one borehole from the surface into a selected (coal) seam wherein a plurality of cavities are formed. The cavities may be formed by chemical, physical or mechanical recovery of the coalxe2x80x9d.
As an example of a technique, which allows the creation of said cavities, Steeman refers to the U.S. Pat. No. 3,961,824 xe2x80x9cMethod and System for Winning Mineralsxe2x80x9d to Wouter Hugo Van Eek. This invention covers a device (scraper) allowing under-reaming a borehole and thus creating the required extended cavity.
The Steeman method works as follows: A borehole is drilled from the surface and then deviated, penetrating into a production interval under a small angle to the horizon in the downward direction. Then a mining device is inserted through the borehole in to the working zone. This mining device consists of a working head, having numerous zigzag folding, mainly hollowed cylindrical sections, armored with rock-breaking scraping elements. This working head is attached to a drill pipe string extending to the surface. To fold this scraper in the working (zigzag) position, a cable is attached to the furthest folding section of the tool. The other end of this cable reaches the surface, and thus can be operated from there. Instead of the cable, a second duct-pipe may be installed inside the tool. This pipe may not only fold but also stretch the working head back to a transporting position.
Once introduced into the hole, the mining tool is slid up and down and slowly folded, so that the cutting elements begin to widen the borehole. The high-pressure water is pumped from the surface down through the tool. At its very bottom it has at least water-jet nozzle. This nozzle serves two main purposes. First, to help the mechanical cutting elements by hydro-jet cutting of rock, and second, to remove created slurry by circulation of this liquid through the well. The inner pipe may have a direct connection to said nozzle(s) and supply high-pressure water. Thus, one of this tool""s embodiments includes a dual wall structure and may have two channels, inner pipe and an annulus between these two pipes, one for working water supply, the second for slurry removal.
According to Steeman, the scraper increases the size of the borehole within the working interval to some xe2x80x9cnear-collapse conditionsxe2x80x9d. The collapse xe2x80x9coccurs suddenlyxe2x80x9d causing development of a fissure system. This system opens access to methane and thus intensifies its production.
The first disadvantage of the Steeman method is uncertainty of technological characteristics, which lowers its application reliability. According to Van Eek, the scraper under-reamer increases the size of the borehole within the working interval to xe2x80x9cnear-collapse conditionsxe2x80x9d. These xe2x80x9cnear-collapse conditionsxe2x80x9d are the uncertainty. Practically, rock-mechanical characteristics of natural strata (such as hardness and stability) are not consistent even within a small area of the ore body. Thus, the cavity may collapse before its completion is accomplished and the scraper is removed from the borehole. It will damage the equipment or even cause loss of it. On the other hand, the span of a created cavity may be not enough for its collapse (too stable of an interval) even by repetitive reversing of the water pressure in the cavity, as is offered by Steeman. The method also has low reliability due to employing a mechanical mining device having numerous parts, sub-assemblies, hardware, fasteners and other units.
The second disadvantage of the Steeman method is its limited application area due to the following two reasons:
1) It requires very consistent rock physical characteristics (hardness and stability) along the cavity development direction, which is practically impossible to find in natural conditions.
2) Since the scraper is a mechanical device, the size of created cavities has a limitation which is equal to the scraper""s section length in collapsed (zigzagged) position. Practically, it means that the span can reach maximum 1.5-2.0 m, which may not be enough for collapse nor for the storage purposes. Meanwhile, the size of the cavity may play a pivotal role since its collapse is further expected.
The third disadvantage is uncertainty of slot orientation. Unlike rotational under-reaming, the scraping of a borehole while folding the device widens its profile in two opposite directions or creates a slot with substantially parallel walls. For the expected further collapse, it is very important that this slot will be oriented in a horizontal position. The closer a slot is to the vertical orientation, the more stable it is and thus its collapse is less likely. As mentioned earlier, the bottom portion of a drill string may twist relatively to its upper end. The deeper the borehole, the more twisting that may occur. In deviated boreholes this twisting is even more likely. Meanwhile, the described device does not provide any information about the orientation of the working head (scraper), so the driving slot orientation is unknown. This further lowers the method""s reliability and repeatability.
The fourth disadvantage is water jet effectiveness. According to the invention, the working head contains at least one nozzle. It is supposed that the water jet will improve (accelerate) the cutting process as it will cut rock along with the mechanical means. It probably will, but not very effectively due to the fact that the borehole is filled with the water/slurry and therefore the jet will be flooded. In comparison to a discharge into a xe2x80x9cdryxe2x80x9d environment, this will decrease jet""s effective cutting radius up to 6 to 10 fold, so the jet will perform all expected functions except effective rock cutting.
The fifth disadvantage is tool complexity. From the patent drawing, the pulling cable, which is supposed to fold a zigzag scraper, is put inside the tool sections and further up the pipe string. That means that the tool assembly (including a pipe string) will be significantly complicated, since in practice it is very difficult to attach (detach) pipes to (from) each other, while having an extended cable inside. In short, the mining device assembly/disassembly is a very complicated procedure.
To overcome the problems of the patents discussed above requires the development of a technology that allows the creation of cavities through gently sloped boreholes. This technique must also effectively create cavities in/through strata with variable characteristics. A remote water jet technology, such as Borehole Mining, applied through sloped boreholes is a solution to the above-mentioned problems and requirements. These boreholes can be deviated from vertical boreholes, if drilled from the land or water surface, or straight, if drilled from underground mines, open pit floors, valleys and other similar workings.
Borehole mining as a remote operated technology is well known and has been developed during recent decades. It adds to an existing mining technological arsenal and decreases environmental impact. However, BHM is not free from certain disadvantages, slowing its further adoption in modern mining, environmental and other industries. One of these disadvantages is the expense of drilling the borehole, which can be 10-25 times the cost of the actual mining. Thus, any decrease of this ratio would significantly improve the effectiveness BHM.
A near-horizontal borehole mining technology can solve the problems left unsolved by known art. This type of borehole could penetrate an irregular-shaped ore body along its longest axis and eliminate numerous vertical access-wells. If underground workings are available, there is no need for deviated boreholes. In this case, only a straight borehole is required. This BHM technique will allow quick and cost-effective access to remote pockets, horizontal seams, and other ore whose development by today""s traditional technologies is not economic.
The primary purpose of this invention is the development of non-vertical or, more specifically, near-horizontal borehole mining technology. It allows for drilling boreholes along the production layer and then extracting material without drilling new boreholes xe2x80x9cback-to-backxe2x80x9d. It also allows employment of a multi-directional drilling technology offering a spoke-like set of deviated boreholes driven through the same mother-well. This significantly decreases the cost of drilling operations and thereby decreases the overall cost of the entire process. The other important aspect of the horizontal BHM is an increase in safety, since the mining and thus collapsing zones will be moved far away from the drill rig and personnel operating site. To realize this idea, horizontal techniques and equipment should be developed, allowing effective extraction of different mineral materials in a wide variety of hydro-geological and environmental conditions.
The accompanying drawings illustrate preferred embodiments of the present invention according to the best mode presently devised for making and using the present invention.
FIG. 1 is a side view of four main schematics of the preferred embodiments of the present invention;
FIG. 2 is a graphical representation of relationships between caverns"" span, and time to caverns"" collapse.
FIG. 3 is a graphical representation of the tool manipulation as a function of time;
FIG. 4 illustrates cross-sectional view through the sloped borehole 4, a BHM tool 14 and a cavern 10;
FIG. 5 illustrates driving of a sinking tunnel while removing a BHM tool from a borehole;
FIG. 6 is the same as FIG. 5 with possible trajectories of a water jet 24 and slurry 27;
FIG. 7 illustrates driving of a sinking tunnel while inserting a BHM tool into a borehole;
FIG. 8 is the same as above but with a bottom head xe2x80x9creversexe2x80x9d assembly and detailed schematic of injection of the slurry from a cavern by a water jet;
FIG. 9 illustrates driving of a raising tunnel while removing a BHM tool from a borehole;
FIG. 10 is the same as above but the tool is inserted into a borehole;
FIG. 11 is a cross-sectional view of a double-stroke tunnel;
FIG. 12 is the 3D perspective view of several spoke-shape boreholes;
FIG. 13 illustrates the offshore application of the present invention;
FIG. 14 illustrates the open pit floor application of the present invention;
FIG. 15 presents different techniques applied in development of the single ore body;
FIG. 16 presents a cross-section view of FIG. 15;
FIG. 17 is the top-down application of the present invention;
FIG. 18 shows a BHM tool arrangement for usage in a strictly horizontal borehole;
FIG. 19 is the 3D perspective view of a cross-section driven through the mine drift 50 and the present invention being applied from this drift;
FIG. 20 is a xe2x80x9croom-and-pillarxe2x80x9d application of the present invention
FIG. 21 illustrates a development of a 60 degrees-sloped seam through the single motherwell;
FIG. 22 illustrates a technique allowing connection of tunnels 10 driven from different boreholes.
FIG. 23 illustrates technique of connecting tunnels on different elevations